This invention relates to unit bearing motors, and more particularly to a bearing wick for a unit bearing motor.
In certain dynamoelectric machines of the induction motor type, and particularly in many smaller motors, sometimes referred to as unit bearing motors, the motors have a squirrel cage rotor assembly in which the conductor bars for the rotor and the body of the rotor are made from die cast aluminum. Typically, these rotor assemblies include a stack or rotor core of individual laminations constructed from suitable ferro-magnetic material. Each lamination has a central opening and a plurality of so-called satellite openings adjacent its outer margin. The laminations are assembled in a stack and are rotated slightly with respect to one another in the stack so that their central openings are coaxial but so that their satellite openings are skewed relative to one another and so that the satellite openings constitute slots. The lamination stack or core is then placed in a suitable die casting mold and molten aluminum is injected under pressure into the mold so as to surround the core, to fill the mold, and to flow through the skewed slots in the core formed by the satellite openings so as to form the conductor bars of the rotor.
These die case squirrel cage rotors typically have a central opening therethrough and a rotor shaft extending through this opening which is rigidly secured to the rotor so that the shaft rotates with the motor. This central opening may be defined at least in part by the central opening of the laminations and is appreciably larger than the shaft so as to receive a rigid boss of the motor housing. The rotor shaft is received in an opening in the boss and is journaled therein by a suitable journal bearing or the like to rotatably support the rotor on the motor housing. As is typical, a portion of the rotor shaft journaled in the bearing has a helical oil groove formed on its outer surface and the outer end of the shaft rotates in a wick supplied with lubricating oil from a resevoir. Upon rotation of the rotor, the oil grooves in the shaft pick up oil from the wick and move it along the length of the bearing to lubricate it. Upon the oil being discharged from the inner end of the bearing, it is slung outwardly by the centrifugal force of the rotating rotor shaft.
In unit bearing motors currently available, the wick is formed as a washer and has a circular opening through which the rotor fits. The wick absorbs oil from the resevoir and brings the oil toward the wick's central opening where the oil is transferred to the rotor shaft. The oil is pumped by a spinal groove along the rotor shaft to lubricate the bearing. For the oil to be transferred to the rotor shaft, the rotor shaft must contact the wick. Generally, wicks used with such motors are made from fibers and cannot be formed to close specifications. If the opening is too large, the rotor shaft will not contact the wick and will not be adequately lubricated. If the opening is too small, the wick will create too much of a drag on the rotor and decrease performance. Oil is preferably delivered to the rotor shaft at a rate of at least 1.0 cc/hour. It has been found that the wicks currently used often deliver oil at a rate of less than 0.5 cc/hour.
Further, the wicks currently used are made of 100% wool. Wool has long fibers which come loose from the wick. These loose fibers then spool around the rotor shaft and freeze the motor.